Since a resin composition dispersed in water may suppress the content of an organic solvent compared to that of a conventional resin dispersed in solvent, such a resin composition dispersed in water has been employed as an environment-friendly resin in a variety of uses such as water-based coating materials (coating compositions) for vehicles, plastic-molded products, domestic electric appliances, steel products, large scale constructions, aircrafts, building materials, construction materials, tiles, and craft products as well as adhesives, resist, printing ink. In a field of automotive coating compositions such as a clear top coating composition for finishing automobiles among such fields, the resin composition dispersed in water is required to give good appearance, sufficiently stable and excellent coating physical properties, and especially high water resistance and further along with increasing consciousness on environmental issues in recent years, in order to satisfy the requirement of low VOC (volatile organic compounds), a technique realizing sufficient reduction in the content of an organic solvent has been longed for.
With regard to a conventional resin dispersed in water, Japanese Kokai Publication Hei-6-192341 (pp 2-3) discloses a long-chain (meth)acrylate copolymer latex obtained in the following manner: a mixture of a long-chain alkyl (meth)acrylate and a hydrophilic monomer is emulsified and dispersed in an aqueous emulsifier solution to form monomer liquid droplets 5 μm or less and the monomer liquid droplets is polymerized. Japanese Kokai Publication 2000-313863 (pp 2-3) discloses an emulsion type adhesive composition obtained in the following manner: a monomer mixture containing a long-chain alkyl (meth) acrylate with an alkyl group having 9 to 13 carbon atoms and an α,β-unsaturated monocarboxylic acid or dicarboxylic acid is emulsified and dispersed in an aqueous radically polymerizable emulsifier solution to form monomer liquid droplets having an average particle diameter of 2 μm or less, and the monomer liquid droplets is polymerized in the presence of an initiator. Japanese Kokai Publication Hei-5-170805 (p 2) discloses an aqueous resin emulsion obtained by emulsion polymerizing a (meth)acrylate of an alcohol having 8 to 30 carbon atoms and other copolymerizable vinyl monomers in an aqueous medium using two kinds of nonionic surfactants having a specific HLB. Japanese Kokai Publication Hei-6-322007 (pp 2-4) discloses an aqueous resin dispersion solution obtained by emulsion polymerizing a polymerizable monomer with an alkyl group having 12 to 18 carbon atoms and other polymerizable monomers in the presence of a high-molecular emulsifier. These resin compositions are obtained by using a highly hydrophobic long-chain alkyl(meth)acrylate as a monomer component and by dispersing the monomer component in an aqueous solvent using an emulsifier or the like to polymerize the monomer component and there is therefore a room for contrivance to more improve the appearance of coating film and the properties of coating film as a composition used in, particularly, applications such as paints for automobiles.
Also, Japanese Kokai Publication Hei-6-49367 (pp 2-3 and 5) discloses a resin composition dispersed in water obtained in the following manners: a resin mixture containing two kinds of acrylic resins having a carboxyl group and a hydroxyl group and a water-insoluble compound or resin having a functional group reactive with the above carboxyl group and hydroxyl group is neutralized by a base and then dispersed in water.
It is described that this resin composition comprises an acrylic resin (a) having a low acid value (acid value: 4 to 23) and an acrylic resin (b) having a high acid value, wherein the additive amount of the acrylic resin having a high acid value is as low as 5 to 25 parts by weight and the additive amount of the acrylic resin having a low acid value is 20 to 60 parts by weight. It is considered that the acid value is too low to use the carboxyl group for crosslinking, and satisfactory performance may not be exhibited because of insufficient crosslinking. Also, it is assumed that satisfactory performance may not be obtained because the dispersion stability of the composition after the composition is dispersed in water is insufficient, and an emulsifier is substantially added to improve, for example, dispersion stability and therefore the influence of the emulsifier on the coating film is concerned. In order that the resin composition sufficiently exhibits excellent coating properties such as excellent appearance and high water resistance required for, particularly, automotive coating compositions, reduction or nonuse of additives, such as emulsifiers, that may affect coating films is desired. There was therefore a room for contrivance in this point.
Moreover, in the specification (pp 1-3) of Japanese Patent No. 2683063, a plastic coating resin composition is disclosed, in which the plastic coating resin composition contains a polymer produced by copolymerizing monomer components including a polymerizable unsaturated monomer having a carboxyl group and other polymerizable unsaturated monomers, and addition polymerizable oxazoline and, as required, a polymer produced by (co)polymerizing monomer components including one or more types of other polymerizable unsaturated monomers. Japanese Kokai Publication 2003-155420 (pp 2, and 5-6) discloses a water-based resin composition comprising a combination of an anionic resin and/or an amphoteric resin, a polyvalent oxazoline compound and a polyvalent metal compound. It is described that these resin compositions use a long-chain acryl (meth) acrylate as a monomer component and an oxazoline crosslinking agent. An oxazoline ring may react with a carboxyl group and there was therefore a room for contrivance to more improve storage stability, thereby making a stable composition even in one-package composition, to more improve the dispersion stability of an acrylic resin in water, whereby the composition exhibits excellent appearance and coating properties when it is used in various applications such as coating compositions for automobiles.
In the meantime, Japanese Kokai Publication Hei-6-256715 (pp 2-4) discloses, a coating composition for repairing automobiles comprising a hydroxyl group-containing (meth) acryl copolymer, a polyisocyanate compound and a solvent and containing an organic solvent as a solvent type resin composition. Also, Japanese Kokai Publication 2000-7950 (page 2) discloses, a powder coating resin composition containing, as essential components, a vinyl copolymer comprising a vinyl monomer containing a silyl group, vinyl monomer containing a glycidyl group, a long-chain alkyl (meth) acrylate and a (meth) acrylate having a bulky alkyl group, and an aliphatic dibasic acid as a powder resin composition. In these resin compositions, there was a room for contrivance to exhibit excellent appearance and coating properties such as high water resistance which are required for, particularly, automobile coating compositions and to deal with recent environmental issues.